The best times of year to visit Bora Bora are the months of November and April.
November and April are the shoulder seasons with great weather and is the best time to visit Bora Bora.
May to October are the worst times to visit Bora Bora and is when rain showers are isolated and the number of tourists swells.
So if you go to Bora Bora during May to October there will usually be bad weather and lots of tourists and people so the time in Bora Bora may not be very enjoyable.
As long as you go to Bora Bora during November and April the weather will be much nicer and there will be less people.
I prefer to go places when there will be less people so I would go to Bora Bora either in November or April.